Granular furnace.



PATENTEDDEG. 31, 1907.

H. N. POTTER.

GRANULAR FURNACE.

APPLICATION FILED MAY 14, 1904.

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No. 875,284. PATENTBD DEC. 31. 1907. H. N. POTTER.

GRANULAR FURNACE.

APPLIOATIOH IILED MA: 14, 1904.

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HENRY NOEL POTTER, OF NEW ROCHELLE, NEW YORK, ASSIGNOR TO GEO.WESTINGHOUSE, OF PITTSBURG, PENNSYLVANIA.

GRANULAR FURNACE.

Specification of Letters Patent.

Patented Dec. 31, 1907.

application filed May 14:, 1904. Serial N0- 208,044

To all whom it may concern:

Be it known that I, HENRY NOEL POTTER, a citizen of the United States,and resident of New Rochelle, county of Westchester, State of New York,have invented certain new and useful Granular Furnaces, of which thefollowing is a specification.

I have devised and operated a peculiar form of electric furnace, whichis particularly practicable to such uses as require that an object orcharge be heated under constant supervision, and be immediately removedfrom the furnace upon the occurrence of some reaction or change ofstate. This furnace has been used for roducing, melting and castingvapor lamp e ectrodes of various alloys, such as ferro-aluminium,chromium aluminium, ferro-silicon, silicon copper, and so forth; alsofor baking and hardening VVelsbach mantles, especially the heads of suchmantles; and also for softening and squirting vitrified silica, and fordrawing and sha ing articles of silica.

T 1e arrangement is very chea and handy, is applicable to anyusepossible or atube furnace and has the advantage over ordinary tubefurnaces of not requiring awkwardly heavy currents at very low voltages,and also that of permitting the tube to be heated to its ends instead ofonly its middle portion, as is the case where the ends extend intospecial contacts or terminals.

The invention is illustrated in the accomp anying drawing, in whichFigure 1 represents a section through a furnace parallel to the axis ofthe tube; Fig. 2 shows a section at right angles to the axis of thetube; Fig. 3 is a detail view; Fig. 4 illustrates a form of furnaceparticularly adapted to the treatment of Welsbach mantles; Fig. 4 is anelevation of a mandrel and mantle adapted to be heated by the type offurnace shown in Fig. 4; Fig. 5 is a sectional view of a furnace forsquirting plastic silica into rods and tubes; Fig. 6 is a detail view;Fig. 7 is a sectional view of a furnace, showing its mechanicalconnections; Fig. Sis a sectional view, the section being taken at rightangles to that of Fig. 7; Fig. 9 illustrates a modification, and Figs.10 and 11 show modified details.

Referring to the first figure of the drawings, 1 and 2 are graphiteelectrodes, 3 is a graphite tube. The space surrounding the tube 3 ispacked with a mass of graphite or carbon broken into small granules. Agood material for this purpose consists of coke and this may be improvedby tumbling it together with finely powdered graphite which coats eachgrain of coke and assists in establishing contact from piece to piece.\Vhereever practicable, however, I prefer granular graphite, as it isunlike amorphous carbon in that it does not change its resistance muchwith a change of temperature and, therefore, requires less regulationand attention. in startingup.

In Fig. 2 the confronting faces of the electrodes 1 and 2 are shownserrated, as I find it advantageous to increase the surfaces which arein contact with the granular resistance so as to minimize arcing andconsequent excessive wear at these surfaces. In view of the importanceof this feature, I have devised and constructed several differentarrangements of electrode faces. For example, I have made the facesseparable and renewable pieces mortised, screwed, wedged, or set intothe electrode body. One such construction is illustrated in Fig 3, whereshort removable slabs, 7, 7, 7, of graphite are slipped into slots inthe electrodes 1 and 2 and project into the granular mass. This permitsthe electrodes to be moved forward and backward slightly, therebychanging the pressure upon the granular resistance. By this means, avery effective and sim le method of regulating the current flow t oughthe furnace is provided.

The granular resistance is held in place on the bottom and sides byrefractory walls, 5 and 6, respectively, of carborundum. or othersuitable material. The tube 3 is held in place largely by the granularmaterial, but may also have other supports, which are often anadvantage, as they hold the tube 3 in place while the granularresistance is built up around it.

In Fig. 1, the tube 3 is shown open at both ends, but for meltingoperations and in other particular cases it may be well to have thebottom closed to prevent rapid burning out by reason of air currents. Inthe form of tube which is open at both ends, a cover, 25, is generallyprovided, and should be kept in place during the heating up and coolingdown to minimize the wear by oxidation.

In Fig. 4 the tube there is shown open at the bottom and closed at thetop by a cap, 26, which is buried beneath the granular material. Thisform of furnace is especially suited to the heating of VVelsbachmantles. The mantle is set 011 a form or mandrel, 47, and pushed up frombelow into the hot tube. This form of furnace has advantages also formelting materials which must be kept in a reducing atmosphere of carbonmonoxid during the treatment by heat. In place of the I mantle and formshown in Fig. 4 the melting pot and charge are pushed up from below, aswill be readily understood.

For squirting plastic silica into rods and tubes the furnace is arrangedwith a tube open at both ends as in Fig. 1. A special form of furnacefor this purpose is illustrated in Fig. 5. A press tube, 8, is fittedinto the upper end of the tube 3, the press tube being provided with asupporting shoulder, 9. This press tube 8 has at its lower end acontracted opening, 10, of the size desired in the squirted silica. Itis well to have this opening 10 longer than is necessary to form thesilica .as the latter has a very wearing action and soon enlarges the oening. The upper end of the tube 8 is fitted with a tight cap 11 boredwith an opening connecting to a tube 12 (see Fig. 6) through whichcompressed air is blown. In the tube 12 is an opening, 13, in shunt tothe air current so to speak. In action silica is placed in the tube 8and rendered plastic. When this state is observed the cover 11 is put inplace and the finger placed over the hole 13. The air no longer able toescape through 13, drives the plastic silica through opening 10 and itfalls into a pail of water.

It is obviously possible to provide a lining or inner tube within thetube 3; this lining may be preferably made of a refractory anddiflicultly reducible oxid, there being no irreducible oxid. The speedof destruction of the lining tube may be reduced by keeping it out ofcontact with the carbon tube. This is easily effected in a vertical tubeby hanging the lining tube, of an outer diameter smaller than the innerdiameter of the carbon tube, within the latter. All supports beingrelatively 0601, any accidental polnts of contact will burn away. It maybe thought best to employ a lining tube, as the gains in the life of thefurnace may be more than offset by the lowering of the temperature dueto the presence of the lining. This is a matter for consideration inspecial cases. Naturally the lining tube may project beyond the heatingtube and serve to lead gases to and from the hot zone. Further the gaseswithin the hot zone are ionized and conducting and a current may bepassed through the gas from auxiliary electrodes, as described in aformer case. To make such a furnace convenient to use, particularly fora variety of uses, it is advantageous to assemble its parts in a frame1- g 1 If which shall readily assist in assembling and operating thefurnace. For example, it is necessary in sofne instances to applypressure to the electrodes 1 and 2 tending to force them against thegranulargmass 4. The electrodes themselves should be guided in theiraxial motion and be capable of retraction and .removal. The containingwalls should be held in position. The heat conducted outward through thepacking should be harmlessly dissipated. There should be no danger of ashort circuit between the electrodes 1 and 2 through the frame. It isfrequently an advantage to use the furnace with the tube inclined orhorizontal so that the frame should be supported in bearingspermitting-turning about the axis of the electrodes l and 2 and ofclamping the frame at any desired angle. To all this may be added theadvantage derivable from working under pressure or vacuum or in variousgases.

In Fig. 7 is shown the furnace having a suitable supporting frame, oneend of which consists of a sleeve, 16, through which the rectangularelectrode 2 extends, the struc- 'ture (not shown) at the opposite sidesof the apparatus is the same as that illustrated in Fig. 7. If pressurebe desired from but one side or end, the construction may be simplifiedin ways which need not be illustrated here. The sleeve 16 is cylindricalupon its outside surface and may be rotated in the bearing, 17, which isat the same time a foot or support for the furnace. The sleeve 16 isinsulately clamped against the end of the furnace containing box, 18, bymeans of the ring, 19, and screws, 20, 20. Metallic contact between thesleeve 16 and the bed is prevented by the insulating askets, 21. Afterthe active portions of t e furnace are in place the hole is surroundedby any suitable heat resisting material, 22, which may be in the form ofbricks or loose powder.

In Fig. 7 the bottom of the box 18 is shown providedwith an openin 23,to enable it to be used for squirting silica as specified in connectionwith Fig. 5. The outer end of the electrode 2 is clamped in a block, 24,to which the current conductor is bolted. Pressure is applied to theelectrode 2 by means of the screw 25 going through the nut 26. In *ig. 8a horizontal section through this latter ,device is given. To the sleeve16 is attached a collar, 27, and the said sleeve is provided with a lugat each side. To each lug is attached a spring, 28, which extends toprolongations of the nut 26. Upon turning the screw 25 by means of thehand-wheel, 29, the springs 28 are extended and exert a constantpressure inward on the electrode 2, keeping it constantly in contactwith the granular material 4. In case it is desirable to draw back theelectrode 2 the screw 25 with its nut 26 is simply drawn back bystretching the springs 28, and the entire compression mechanism bentdownward out of the way. i The electrode 2 can then be pulled back. The

supporting feet 17 are mounted in any convenient way and the furnace canthen be operated either in a vertical position as shown, or by turningthe furnace bed about the axis of the electrodes 1 and 2 in the bearing17, the axis 3 can be given any angle for example, it can be madehorizontal or adapted to repeat the experiments described by Moissan.

For special purposes where it is necessary that the tube 3 should beevenly heated the arrangement shown in Fig. 9 may be advantageouslyused. In this we have two sets of electrodes 1 and 2, and 1 and 2,respec tively. The granular resistance is here shown in the form of across having the tube 3 embedded at the middle. The electrodes 1 and 2are connected into one electric circuit, and electrodes 1 and 2* into asecond circuit. These circuits may be entirely independent and suppliedfrom separate machines or storage batteries, or they may be operated bya two-phase machine, 30, as shown in the drawing. It is, of course,obvious that with three electrodes, instead of four, a three phasecircuit with three connect ing wires could be used. Further, it wouldnot be a departure from the spirit of the present invention to use aplurality of tubes embedded in the same granular resistance, nor needthese tubes be necessarily of the same diameter nor their axes beparallel. Moreover, a tube need not be circular in crosssection, and maybe conical or of any convenient shape without adding to the complicationof construction or departing from the invention. I have found that it isof advantage under certain conditions to provide one or more slits inthe tube 3, substantially parallel to the axis of the tube. Thisprevents the current from passing into and around the tube and out onthe other side. I also find that when the furnace is to be operated atvery high temperatures, the tube is liable to become deformed by reasonof the external pressure upon it. In such cases it is found advantageousto provide a tube with one or more rings of graphite for holding it inshape. These modifications are illustrated in Fig. 10, wherein 3 is thetube, slitted at 51, 51, and surrounded by the graphite rings 52, 52. InFig. 11, I show a lining tube, 53, within the tube, 3, and projectingbeyond the same.

I claim as my invention:

1. An electric furnace consisting of a refractory heating resistancecomposed of free granules clamped between refractory electrodes,together with a refractory hollow body embedded within the said granularresistance.

2. An electric furnace consisting of a refraetory heating resistancecomposed of free graphite granules clamped between refractoryelectrodes, together with a refractory hollow body embedded within thesaid granular resistanc'e.

3. An electric furnace consisting of, a granular refractory hollow bodyembedded within a granular refractory heating resistance clamped betweenelectrodes and means for causing one or more electrodes to becontinuously pressed against said granular resistance.

4. An electric furnace consisting of a hollow refractory body embeddedwithin a granular heating resistance, which is held in place byrefractory walls having lower electric conductivity than the saidgranular heating resistance, and by refractory electrodes pressedagainst the said granular heating resistance.

5. An electric furnace consisting of a vertical hollow refractory bodyheld in place by a refractory plate through which said body passes, andpartially surrounded by a heating resistance composed of free granulesretained between refractory walls and pressed between suitableelectrodes.

6. An electric furnace consisting of a hollow refractory body embeddedwithin a granular heating resistance provided with refractory electrodesand surrounded by refractory packing material within a container sosupported as to be capable of turning about an axis substantially atright an les to the axis of the said hollow refractory ody.

7. An electric furnace consisting of a hol low refractory body embeddedwithin a granular heating resistance provided with more than twoelectrodes, said electrodes being so joined to sources of electricpotential that each electrode may supply current to a portion of thesaid granular resistance.

8. An electric furnace consisting of a hollow refractory body embeddedwithin a granular heating resistance, having two pairs of electrodes,the axis of one pair of electrodes being substantially at right anglesto the axis of the other pair, each pair of electrodes being connected.to a source of energy electrically independent of the other.

9. An electric furnace consisting of a hollow refractory body embeddedwithin a granular heating resistance and having two pairs of electrodesconnected respectively to the two sides of a two phase circuit.

10. An electric furnace consistin of a granular heating resistancewithin w rich is embedded a refractory tube of conducting material, theconductivity of which in a direction at right angles to its axis, isdecreased by a slit or slits in the said tube substantially parallel toits axis.

11. An electric furnace consisting of a. granular heating resistancewithin which is embedded a refractory tube built up of a plu rality oflongitudinal segments.

12. An electric furnace having a heating 4: 876,284.- fir resistancecomposed of anular coke; the. Signed at New York in the county of Newgrains of which have een coated with York and State of New York this10th day of 10 graphiff. .1 f f May A. D. 1904.

13. n e eetrle urnace oonsistin 0 a granular heating resistance and arefr actory HENRY NOEL POTTER tube embedded therein, the said tube beingWitnesses: surrounded by one or more supporting WM. H. CAPEL, rings ofgraphite. GEORGE H. STOOKBRIDGE.

